VTL MB-450 "Generations"

I read the following in a 'goner's virtual system (from a 2004 Sterophile review).

"Since Chip Stern's update on VTL's second-generation MB-450 Signature back in October 2002, the amplifier has undergone further changes and improvements. It now features a completely redesigned input stage that incorporates advances made during the development of VTL's mighty Siegfried monoblocks."

This implies to me that there are at least 3 "generations" of this amp.
1 - When first introduced
2 - Available at the time of Oct. 2002 review
3 - Sometime before April 2004 when above line was printed
(they have a new version on the way but I won't count that)

Does anyone know how you could tell what "Generation" you had, serial number? other markings? Can you get a 1G or 2G upgraded to a 3G? If anyone is "in" on the nuances of the MB-450's life I would be interested in learning more.

Thanks for your input.